1. Field of the Invention
This invention relates to weather-resistant, high-impact strength (meth)acrylic compositions useful for producing (meth)acrylic articles or as a capcoat layer for polymeric substates, especially PVC.
2. Prior Art
Acrylic compositions and articles made from them are well known for their clarity, sparkling color, surface gloss and weather resistance. They are also well known for their low-impact strength or brittleness. It has become standard practice to incorporate toughening agents or impact modifiers in acrylic formulations to make them more durable. The incorporation of such functional additives can, however, detract from some of the desirable characteristics of the acrylics, for example the addition of large quantities of rubbery polymers can lower the softening point and contribute to haze.
There have been many attempts to improve the acrylic composition by forming copolymers, which are intended to modify the physical properties of the acrylic polymer. Other approaches include the use of additives intended to improve physical properties such as impact strength, generally known as polymeric impact modifiers. The polymeric impact modifiers include a wide variety of polymers, such as natural and synthetic rubber, acrylate rubbers, and terpolymers such as MBS (methylmethacrylate/butadiene/styrene).
One type of polymeric impact modifier is sequentially polymerized acrylic compositions comprising a core, an intermediate and a final stage, although there can be some intermingling of the “layers”. In general, these are known as “core/shell” polymers.
There are many factors which determine the efficiency and utility of any specific acrylic core/shell impact modifier. These include the matrix in which it is used or the substrate to which it is adhered whether alone or as part of a capstock composition. Also highly influent are the number of layers in each stage, the thickness and construction of each layer, the monomer composition of each layer, the type and degree of crosslinking of each layer, the type and degree of grafting, as well as the concentration of the sequentially polymerized core/shell impact modifier in the matrix or primary polymer. The matrix polymer or primary polymer as defined herein is the polymer which forms the bulk of the articles, such as acrylic sheet, or an extruded capstock.
Specific examples of core/shell impact modifiers can be found in the following referenced patents: U.S. Pat. No. 3,661,994; U.S. Pat. No. 3,793,402; U.S. Pat. No. 4,433,103; U.S. Pat. No. 4,521,568; U.S. Pat. No. 5,270,397; U.S. Pat. No. 6,172,135; U.S. Pat. No. 5,318,737; EP 0,458,520A2; and WO 00/08098.